1. Field of the Invention
The present invention relates to a memory array, particularly to a method for operating a low-cost EEPROM (Electrically Erasable Programmable Read Only Memory) array.
2. Description of the Related Art
The CMOS (Complementary Metal Oxide Semiconductor) technology has been a normal process for fabricating ASIC (Application Specific Integrated Circuit). Flash memories and EEPROM (Electrically Erasable Programmable Memory) have been widely used in electronic products because their data will not volatilize but can be erased and programmed electrically.
Non-volatile memories are programmable, storing charges to vary gate voltages of transistors, or not storing charges to preserve the original gate voltages of transistors. In erasing a non-volatile memory, the charges stored in the non-volatile memory are eliminated to resume the initial state of the memory. The flash memory architecture has advantages of small size and low cost. However, the flash memory architecture does not allow erasing or programming a single one-bit memory cell but allows erasing or programming a block of the memory. Therefore, the flash memory architecture is inconvenient in application. The EEPROM architecture supports a “byte write” function. Thus, the EEPROM architecture is more convenient than the flash memory architecture. Refer to FIG. 1 and FIG. 2 respectively schematically showing a circuit and a sectional view of a one-bit memory cell of the conventional EEPROM architecture. As shown in FIG. 1 and FIG. 2, the one-bit memory cell of the EEPROM architecture is a polysilicon memory cell and comprises a memory transistor 10, a selection transistor 12 and a capacitor structure disposed above the memory transistor 10. Because of the abovementioned memory cell structure, EEPROM occupies larger area than the flash memory. Besides, in bit erasing of EEPROM, the transistors at the unselected positions must be separated. Thus, the cost of using EEPROM is increased.
In order to overcome the abovementioned problems of the conventional technology, the Inventors develop a low-cost EEPROM array and propose a method for operating the same and massively programming the memory cells of the same simultaneously.